Systems and methods for electrophotography-based additive manufacturing of parts utilizing multiple printing paths

ABSTRACT

An electrophotography-based additive manufacturing system (e.g.,  10; 100; 200; 300; 350; 500; 700 ) having at least one electrophotography (EP) or electrostatographic engine (e.g.,  12; 12   p;    12   s;    612   p;    612   p;    712 - 1; 712 - 2 ) and being configured such that a plurality of independently movable parts is built in parallel at a plurality of decoupled processing stations.

BACKGROUND

The present disclosure relates to additive manufacturing systems for printing three-dimensional (3D) parts. In particular, the present disclosure relates to additive manufacturing systems and processes for building 3D parts and support structures using an imaging process, such as electrophotography.

Additive manufacturing is generally a process in which a three-dimensional (3D) object is manufactured based on a computer image of the object. A basic operation of an additive manufacturing system consists of slicing a three-dimensional computer image into thin cross sections, translating the result into two-dimensional position data, and feeding the data to control equipment which manufacture a three-dimensional structure in a layer wise manner using one or more additive manufacturing techniques. Additive manufacturing entails many different approaches to the method of fabrication, including fused deposition modeling, ink jetting, selective laser sintering, powder/binder jetting, electron-beam melting, electrophotographic imaging, and stereolithographic processes.

In an electrophotographic 3D printing process, each slice of the digital representation of the 3D part and its support structure is printed or developed from powder materials using an electrophotographic engine. The electrophotographic engine generally operates in accordance with 2D electrophotographic printing processes, using charged powder materials that are formulated for use in building a 3D part (e.g., a polymeric toner material). The electrophotographic engine (“EP engine”) typically uses a support drum that is coated with a photoconductive material layer, where latent electrostatic images are formed by electrostatic charging following image-wise exposure of the photoconductive layer by an optical source. (Alternatively, an image may be formed using ionography by direct-writing electrons or ions onto a dialectric, and eliminating the photoconductor, all within the scope of the present invention and within the use of the electrophotography terminology as used herein). The latent electrostatic images are then moved to a developing station where the polymeric toner is applied to charged areas, or alternatively to discharged areas of the photoconductive insulator to form the layer of the charged powder material representing a slice of the 3D part. The developed layer is transferred to a transfer medium, from which the layer is transfused to previously printed layers with heat and/or pressure to build the 3D part.

Electrophotographic 3D printing as part of a manufacturing process can be embedded in a manufacturing flow. However, due to the use of a transfusion process for the manufacture of a part-in-process, significant time can be lost in repeatedly positioning the part for the transfusion step(s) where heat and pressure are used to transfuse printed layers onto a build surface of a part. As a result, the EP engine may only be utilized a portion of the time, and the overall processing rate can be low as a result.

SUMMARY

Aspects of the present disclosure are directed to an electrophotography-based or electrostatographic-based additive manufacturing system having at least one electrophotography (EP) or imaging engine or and being configured such that a plurality of independently movable parts are built in parallel at a plurality of decoupled processing stations.

Other aspects of the present disclosure are directed to an electrophotography-based additive manufacturing system comprising a first EP transfuser and a gantry with a single x-stage having at least two x-stage actuators each configured to move a different one of a plurality of independently movable parts in the x-direction under the first EP transfuser.

Other aspects of the present disclosure are directed to an electrophotography-based additive manufacturing system comprising a first EP transfuser and a gantry with a first x-stage and a second x-stage each configured to move a different one of a plurality of independently movable parts in the x-direction, the system configured to move the first and second x-stages in a y-direction such that the first x-stage is positioned under the first EP transfuser and then the second x-stage is positioned under the first EP transfuser.

Other aspects of the present disclosure are directed to an electrophotography-based additive manufacturing system comprising a part transport system with a track along which a plurality of independently moveable parts move between decoupled processing stations in both an x-direction and a y-direction. The system can further have a single Z-stage configured to move the track in a Z-direction, or a plurality of Z-stages each configured to move a different one of the plurality of parts in a Z-direction relative to the track.

Other aspects of the present disclosure are directed to an electrophotography-based additive manufacturing system comprising a plurality of part paths along which a plurality of independently moveable parts move between the decoupled processing stations. The system can further comprise a plurality of Z-stages, with each of the plurality of parts configured to move along the plurality of part paths on a separate one of the plurality of Z-stages.

Other aspects of the present disclosure are directed to an environmentally controlled chamber for transporting an additive manufactured part through two or more spatially separated processes, one of those processes being an electrostatic-additive process.

DEFINITIONS

Unless otherwise specified, the following terms as used herein have the meanings provided below:

The term “copolymer” refers to a polymer having two or more monomer species, and includes terpolymers (i.e., copolymers having three monomer species).

The terms “at least one” and “one or more of” an element are used interchangeably, and have the same meaning that includes a single element and a plurality of the elements, and may also be represented by the suffix “(s)” at the end of the element. For example, “at least one polyamide”, “one or more polyamides”, and “polyamide(s)” may be used interchangeably and have the same meaning.

The terms “transfusion”, “transfuse”, “transfusing”, and the like refer to the adhesion of layers with the use of heat and pressure, where polymer molecules of the layers at least partially interdiffuse.

The term “transfusion pressure” refers to a pressure applied during a transfusion step, such as when transfusing layers of a 3D part together.

The term “deformation temperature” of a 3D part refers to a temperature at which the 3D part softens enough such that a subsequently-applied transfusion pressure, such as during a subsequent transfusion step, overcomes the structural integrity of the 3D part, thereby deforming the 3D part.

Unless otherwise specified, temperatures referred to herein are based on atmospheric pressure (i.e. one atmosphere).

The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the present disclosure.

Directional orientations such as “above”, “below”, “top”, “bottom”, and the like are made with reference to a direction along a printing axis of a 3D part. In the embodiments in which the printing axis is a vertical Z-axis, the layer-printing direction is the upward direction along the vertical Z-axis. In these embodiments, the terms “above”, “below”, “top”, “bottom”, and the like are based on the vertical Z-axis. However, in embodiments in which the layers of 3D parts are printed along a different axis, the terms “above”, “below”, “top”, “bottom”, and the like are relative to the given axis.

The term “providing”, such as for “providing a material” and the like, when recited in the claims, is not intended to require any particular delivery or receipt of the provided item. Rather, the term “providing” is merely used to recite items that will be referred to in subsequent elements of the claim(s), for purposes of clarity and ease of readability.

Unless otherwise specified, temperatures referred to herein are based on atmospheric pressure (i.e. one atmosphere).

The terms “about” and “substantially” are used herein with respect to measurable values and ranges due to expected variations known to those skilled in the art (e.g., limitations and variabilities in measurements).

All references cited herein are incorporated by reference in their entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram of an exemplary conventional electrophotography-based additive manufacturing system for printing 3D parts and associated support structures.

FIG. 1A is a schematic front view of an exemplary transfusion assembly for performing layer transfusion steps with the developed layers.

FIG. 2 is a schematic view of a first example embodiment of a multipath transfusion/build process system according to the present disclosure having a single x-stage and two x-stage actuators.

FIG. 3 is a schematic view of a second example embodiment of a multipath transfusion/build process system according to the present disclosure having dual x-stages.

FIG. 3a is a schematic view of another multi-path transfusion assembly according to the present disclosure having dual x-stages.

FIG. 4 is a schematic view of a third example embodiment of a multipath transfusion/build process system according to the present disclosure having a continuous track along which parts move in the x-direction and the y-direction.

FIG. 5 is a schematic view of a multipath transfusion/build process system having individually enabled gantries in a Z direction.

FIG. 6 is a diagrammatic perspective view of an environmentally controlled chamber for transporting an additive manufactured part through two or more spatially separated processes.

FIG. 7 is a flow chart of a method for printing a part in accordance with exemplary embodiments.

FIG. 8 is a schematic front view of a pair of electrophotography engines of the system for developing layers of the part and support materials.

FIG. 9 is a schematic front view of an alternative electrophotography engine, which includes an intermediary drum or belt.

FIG. 10 is a schematic view of an example embodiment of a multipath system according to the present disclosure having a continuous track along which parts move in the x-direction and the y-direction with EP engines developing layers directly on part surfaces.

DETAILED DESCRIPTION

The present disclosure is directed to electrophotography-based or electrostatographic-based additive manufacturing systems for printing 3D parts, and methods of printing 3D parts using the systems in a manufacturing process. In exemplary embodiments, the multi-path systems and configurations are implemented to utilize a higher percentage of the processing rate capabilities of the electrophotography (EP) engine(s), enable decoupling of the sequential unit operations which are rate-limiting, and thereby increase the overall processing rate of the manufacturing process.

As mentioned above, during a electrophotographic 3D part additive manufacturing or printing operation, an EP engine may develop each layer of the 3D part (and any associated support material) out of a polymeric toner or powder-based material using the electrophotographic process. The developed layers are then transferred to a transfer medium, which delivers the layers to a transfusion assembly where the layers are transfused (e.g., using heat and/or pressure) to build a 3D part and support structures in a layer-by-layer manner.

FIG. 1 is a simplified diagram of an exemplary electrophotography-based additive manufacturing system 10 for printing 3D parts and associated support structures, in accordance with embodiments of the present disclosure. As shown in FIG. 1, system 10 includes one or more EP engines, generally referred to as 12, such as EP engines 12 p and 12 s, a transfer assembly 14, biasing mechanisms 16, and a transfusion assembly 20. Examples of suitable components and functional operations for system 10 include those disclosed in Hanson et al., U.S. Pat. Nos. 8,879,957 and 8,488,994, and in Comb et al., U.S. Patent Publication Nos. 2013/0186549 and 2013/0186549.

The EP engines 12 p and 12 s are imaging engines for respectively imaging or otherwise developing layers, generally referred to as 22, of the powder-based part and support materials, where the part and support materials are each preferably engineered for use with the particular architecture of the EP engine 12 p or 12 s. As discussed below, the developed layers 22 are transferred to a transfer medium 24 of the transfer assembly 14, which delivers the layers 22 to the transfusion assembly 20. The transfusion assembly 20 operates to build the 3D part 26, which may include support structures and other features, in a layer-by-layer manner by transfusing the layers 22 together on a build platform 28, which is configured in FIG. 1 as a reciprocating x-stage.

In some embodiments, the transfer medium 24 includes a belt, as shown in FIG. 1. Examples of suitable transfer belts for the transfer medium 24 include those disclosed in Comb et al., U.S. Patent Application Nos. 2013/0186549 and 2013/0186558. In some embodiments, the belt 24 includes front surface 24 a and rear surface 24 b, where front surface 24 a faces the EP engines 12, and the rear surface 24 b is in contact with the biasing mechanisms 16. In other embodiments, the transfer medium can include a plurality of belts or individual sheets onto which one or more layers of a part are printed or a layer of multiple part(s) is printed onto a single sheet.

In some embodiments, the transfer assembly 14 includes one or more drive mechanisms that include, for example, a motor 30 and a drive roller 33, or other suitable drive mechanism, and operate to drive the transfer medium or belt 24 in a feed direction 32. In some embodiments, the transfer assembly 14 includes idler rollers 34 that provide support for the belt 24. The exemplary transfer assembly 14 illustrated in FIG. 1 is highly simplified and may take on other configurations. Additionally, the transfer assembly 14 may include additional components that are not shown in order to simplify the illustration, such as, for example, components for maintaining a desired tension in the belt 24, a belt cleaner for removing debris from the surface 24 a that receives the layers 22, and other components.

The EP engine 12 s develops layers of powder-based support material, and the EP engine 12 p develops layers of powder-based part material. In some embodiments, the EP engine 12 s is positioned upstream from the EP engine 12 p relative to the feed direction 32, as shown in FIG. 1. In alternative embodiments, the arrangement of the EP engines 12 p and 12 s may be reversed such that the EP engine 12 p is upstream from the EP engine 12 s relative to the feed direction 32. In further alternative embodiments, system 10 may include three or more EP engines 12 for printing layers of additional materials, as indicated in FIG. 1.

System 10 also includes controller 36, which represents one or more processors that are configured to execute instructions, which may be stored locally in memory of the system 10 or in memory that is remote to the system 10, to control components of the system 10 to perform one or more functions described herein. In some embodiments, the controller 36 includes one or more control circuits, microprocessor-based engine control systems, and/or digitally-controlled raster imaging processor systems, and is configured to operate the components of system 10 in a synchronized manner based on printing instructions received from a host computer 38 or a remote location. In some embodiments, the host computer 38 includes one or more computer-based systems that are configured to communicate with controller 36 to provide the print instructions (and other operating information). For example, the host computer 38 may transfer information to the controller 36 that relates to the sliced layers of the 3D parts and support structures, thereby allowing the system 10 to print the 3D parts 26 and support structures in a layer-by-layer manner

The components of system 10 may be retained by one or more frame structures. Additionally, the components of system 10 may be retained within an enclosable housing that prevents components of the system 10 from being exposed to ambient light during operation.

In an exemplary embodiment, the EP engines 12 s and 12 p can include a photoconductive drum with a photoconductive surface 46. The photoconductive surface 46 is a thin film extending around the circumferential surface of the conductive drum body 44, and the surface 46 is configured to receive latent-charged images of the sliced layers of a 3D part or support structure (or negative images), and to attract charged particles of the part or support material to the charged or discharged image areas, thereby creating the layers of the 3D part or support structure.

An imager 56 is a digitally-controlled, pixel-wise light exposure apparatus configured to selectively emit electromagnetic radiation toward the uniform electrostatic charge on the surface 46 as the surface 46 rotates in the direction 52 past the imager 56. The selective exposure of the electromagnetic radiation to the surface 46 is directed by the controller 36, and causes discrete pixel-wise locations of the electrostatic charge to be removed (i.e., discharged to ground), thereby forming latent image charge patterns on the surface 46. Each development station 58 may also include one or more devices for transferring the charged part or the support material 66 p or 66 s to the surface 46, such as conveyors, fur brushes, paddle wheels, rollers, and/or magnetic brushes. For instance, as the surface 46 (containing the latent charged image) rotates from the imager 56 to the development station 58 in the direction 52, the charged part material 66 p or the support material 66s is attracted to the appropriately charged regions of the latent image on the surface 46, utilizing either charged area development or discharged area development (depending on the electrophotography mode being utilized). This creates successive layers 22 p or 22 s as the photoconductor drum 12 continues to rotate in the direction 52, where the successive layers 22 p or 22 s correspond to the successive sliced layers of the digital representation of the 3D part or support structure.

The successive layers 22 p or 22 s are then rotated with the surface 46 in the direction 52 to a transfer region in which layers 22 p or 22 s are successively transferred from the photoconductor drum 42 to the belt 24 or other transfer medium. While illustrated as a direct engagement between the photoconductor drum 42 and the belt 24, in some preferred embodiments, the EP engines 12 p and 12 s may also include intermediary transfer drums and/or belts.

The EP engine 12 p may also include an intermediary drum 42 a that rotates in the direction 52 a that opposes the direction 52, in which drum 42 is rotated, under the rotational power of motor 50 a. The intermediary drum 42 a engages with the photoconductor drum 42 to receive the developed layers 22 p from the photoconductor drum 42, and then carries the received developed layers 22 p and transfers them to the belt 24.

The EP engine 12 s may include the same arrangement of an intermediary drum 42 a for carrying the developed layers 22 s from the photoconductor drum 42 to the belt 24. The use of such intermediary transfer drums or belts for the EP engines 12 p and 12 s can be beneficial for thermally isolating the photoconductor drum 42 from the belt 24, if desired.

Utilizing EP techniques for printing one or more 3D parts is a manufacturing process, which requires the printing to be embedded in a manufacturing flow. From a hardware standpoint, this means enabling more positioning capability of the part-in-process than just back-and-forth through the transfusing step. Also, the maximum processing rate for an EP engine is much greater than that of the transfusion process. As such, decoupling the EP imaging from the transfusion step will increase the overall processing rate.

Previously, it was typical to utilize multiple EP engines with a single belt and transfusion assembly to print in a single stack on a reciprocating x-stage. The prior reciprocating x-stage allows about 40% utilization of the EP engines. This was due to the existence of blank space, between image frames on the belt, which was somewhat longer than each image frame and which was required to register subsequent imaged layers. The present disclosure includes systems and methods which utilize one or more EP engines, one or more transfusion assemblies, multiple platens or build platforms, and a part transport system providing multiple part paths along a “track” to print multiple parts in parallel to accelerate the printing process. It must be understood that the term “platen” can refer to a removable feature of a build platform, or can more generally refer to the build platform itself and not to a removable component.

In exemplary embodiments, multiple platens or build platforms are moved in the x-direction and y-direction along part paths provided by “tracks” of a part transport system such that any one transfusion assembly is used in an alternating fashion to transfuse layers onto multiple parts such that the build process occurs simultaneously or in parallel in that one part is not completed before the transfusion assembly is used in the build of another part. Further, in some exemplary embodiments, multiple transfusion assemblies are utilized along the part paths such that different layers of a part are transfused by different transfusion assemblies. The “tracks” can be any mechanical system or part transport system which moves the platens along predefined paths in the x-direction and the y-direction, for example a rail system as well as any components (e.g., sprocket driven chains, motors, etc.) which move the platens along the path(s) in the x-direction and y-directions, while providing sufficient support in the z-direction to withstand the pressure applied by the transfusion assemblies during the layer transfusion process.

FIG. 1A illustrates an exemplary embodiments of the layer transfusion assembly 20. In order to illustrate the transfusion process using a transfusion assembly, transfusion assembly 20 is described in the context of a single transfusion assembly transferring layers sequentially on a single part supported by a gantry 80. The disclosed concepts of the multiple part paths is therefore not illustrated in FIG. 1A, and will be described in greater detail below.

Embodiments of the transfusion assembly 20 can include a pressing component 70, pre-transfusion heaters 72 and 74, and a post-transfusion cooler 76. Other embodiments do not include the post-transfusion cooler 76, and instead the cooling of the part can occur after transfusion. The build platform 28 is a platform assembly or platen that is configured to receive the heated combined layers 22 (or separate layers 22 p and 22 s) for printing the structure 26, which includes a 3D part 26 p formed of the part portions 22 p, and support structure 26 s formed of the support structure portions 22 s, in a layer-by-layer manner. In some embodiments, the build platform 28 may include removable film substrates (not shown) for receiving the printed layers 22, where the removable film substrates may be restrained against the build platform 28 using any suitable technique (e.g., vacuum, clamping or adhering). In some exemplary embodiments disclosed further below, multiple platens or build platforms are utilized to move parts through one or more paths to allow multiple parts to be printed together or at the same time (e.g., alternating layers printed by the same transfusion assembly on different parts, different layers of a single part to be printed by different transfusion assemblies, etc.), and the build platform need not be the same as shown in FIGS. 1 and 1A.

In the illustrated example, the platen or build platform 28 is supported by a gantry 80, or other suitable mechanism, which is configured to move the platform 28 along the z-axis and the y-axis, as illustrated schematically in FIGS. 1 and 1A, and optionally along the x-axis that is orthogonal to the y and z axes. In embodiments discussed below with reference to FIGS. 2-5, the build platform is moved in the x-direction (or along the x-direction and y-direction) along one or more tracks or paths of a part transport system such that the build platform and part are acted on by the same transfusion assembly in an alternating fashion with other parts being built, or such that the build platform and part are moved to be acted on by multiple transfusion assemblies. In these embodiments, the gantry 80 can be considered to be a component of the part transport system providing the track or paths, as well as any components (e.g., sprocket driven chains, motors, etc.) which move the build platform along the path(s) in the x-direction and y-direction. The gantry 80 can also include a mechanism 83, such as a piston mechanism, a screw driven jack, or other linear actuator, configured to lower the build platform as successive developed layers are transferred to the part build surface by a transfusion assembly.

As shown as an example of transfusion assembly functionality in FIG. 1A, the part transport system or gantry 80 includes a y-stage gantry 82 that is configured to move the platen or build platform 28 along at least the y-axis, and an x-stage gantry 84 that is configured to move the build platen or platform 28 along the x-axis. Again, the y-stage gantry and the x-stage gantry can be in the form of tracks or mechanical paths, along with any mechanisms or devices which move the platens or build platform along the tracks or paths in the x-direction, the y-direction, and combinations of the x-direction and the y-direction. The gantry 80 may include a z-stage gantry 83 that is configured to move the build platform along the z-axis. In this illustrative embodiment, the y-stage gantry 82 may be operated by a motor 85, and the x-stage gantry 84 may be operated by a motor 86, based on commands from the controller 36. The motors 85 and 86 may each be any suitable actuator an electrical motor, a hydraulic system, a pneumatic system, piezoelectric, or the like. As mentioned above, the z-stage gantry 83, shown diagrammatically in FIG. 1A, can be any type of actuator or actuators (e.g., linear actuators such as piston(s), jacks, etc.) which lower the build platform as successive developed layers are transfused (including heating, applying pressure, and optionally cooling) onto the part build surface 88, which is the top surface of the printed structure 26.

In the example embodiment of FIG. 1A, the y-stage gantry 82 supports the x-stage gantry 84, or vice versa. In some embodiments, the y-stage gantry 82 is configured to move the platen or build platform 28 and the x-stage gantry 84 along the z-axis and the y-axis. For example, the y-stage gantry 82 produces a reciprocating rectangular pattern where the primary motion is back-and-forth along the y-axis, as illustrated by broken lines 87 in FIG. 1A. While the reciprocating rectangular pattern is illustrated as a rectangular pattern with sharp axial corners (defined by arrows 87), y-stage gantry 82 may move the platen or build platform 28 in a reciprocating rectangular pattern having rounded or oval corners, so long as the build platform 28 moves along the y-axis process direction (illustrated by arrow 87 a) during the pressing steps at the pressing component 70 described below. As described further below, the x-stage gantry and the y-stage gantry, which can be implemented together, move the build platform and part along paths in the x-direction and z-direction, and those paths can include sharp or rounded corners as well. Further, the paths can be piecewise linear paths formed of linear segments.

In some embodiments, the platen or build platform 28 is heated using a heating element 90 (e.g., an electric heater). The heating element 90 is configured to heat and maintain the build platform 28 at an elevated temperature that is greater than room temperature (25° C.), such as at a desired average part temperature of 3D part 26 p and/or support structure 26 s, as discussed in Comb et al., U.S. Publication Nos. 2013/0186549 and 2013/0186558. This allows the build platform 28 to assist in maintaining 3D part 26 p and/or support structure 26 s at this average part temperature. However, it must be noted that heating of platen or build platform 28 is not required in all embodiments.

In some embodiments, the pressing component 70 is configured to press the layers 22 from a belt to the build surface 88 of the structure 26 to transfuse the layers 22 to the build surface 88. In some embodiments, the pressing component 70 is configured to press each of the developed layers 22 on the belt 24 or other transfer medium into contact with the build surfaces 88 of the structure 26 on the build platform 28 for a dwell time to form the 3D structure 26 in a layer-by-layer manner While a single part or structure 26 is shown in FIG. 1A, as discussed above and as will be discussed in further detail below, multiple platens or build platforms and parts can be printed at the same time and the different individual layers 22 on the belt 24 of any one transfusion assembly can be designated for, and transferred to, different parts. Similarly, consecutive individual layers printed onto a particular part can be printed onto the build surface of the part by different transfusion assemblies.

The pressing component 70 of a transfusion assembly may take on any suitable form. In some exemplary embodiments, the pressing component 70 is in the form of a nip roller, as shown in FIG. 1A. The pressing component 70 can include a pressing plate, such as discussed in Comb et al., in U.S. Pub. Nos. 2013/0186549 and 2013/0075033, which are each incorporated by reference in their entirety. In some exemplary embodiments, the pressing component 70 includes the support of the belt 24 between pairs of rollers, such as discussed in Comb et al., in U.S. Pub. Nos. 2013/0186549 and 2013/0075033. The pressing component 70 may also take on other suitable forms. Thus, while embodiments will be described below using the nip roller embodiment of the pressing component 70, it is understood that embodiments of the present disclosure include the replacement of the nip roller with another suitable pressing component 70. It will be further understood that while example components of one transfusion assembly 20 are discussed, multiple transfusion assemblies can be included within the system along the part path(s) as described below.

In some embodiments, the nip roller 70 is configured to rotate around a fixed axis with the movement of the belt 24. In particular, the nip roller 70 may roll against the rear surface 24 b in the direction of arrow 92, while the belt 24 rotates in the feed direction 32.

In some embodiments, the pressing component 70 includes a heating element 94 (e.g., an electric heater) that is configured to maintain the pressing component 70 at an elevated temperature that is greater than room temperature (25° C.), such as at a desired transfer temperature for the layers 22.

In some embodiments, the pre-transfusion heater 72 includes one or more heating devices (e.g., an infrared heater and/or a heated air jet) that are configured to heat the layers 22 on the belt 24 to a temperature near an intended transfer temperature of the layer 22, such as at least a fusion temperature of the part material 66 p and the support material 66 s, prior to reaching nip roller 70. Each layer 22 desirably passes by (or through) the heater 72 for a sufficient residence time to heat the layer 22 to a temperature that is typically below a temperature required to transfuse the layer onto the previously printed layers. In other embodiments, layers 22 are either not heated, or are heated but to a temperature lower than the fusion temperature of the part material and then are pressed into a part build surface which has been rapidly heated to a temperature in a range between the flowable temperature and a thermal oxidation threshold temperature for the part material, such that the heated temperature is at or above the flowable temperature and below the thermal oxidation threshold. If layers 22 are not heated, heater 72 can be optionally omitted in some embodiments.

When the part material and/or support material is an amorphous polymer, the polymer does not have a melting point, but rather becomes flowable or molten as the temperature rises. In contrast, a semi-crystalline material has a melting point where the semi-crystalline material becomes flowable. While the present disclosure references amorphous polymers, it is understood that the present disclosure can be utilized with semi-crystalline materials.

The pre-transfusion heater 74 is typically a non-contact heater that heats the top surfaces of the 3D part 26 p and support structure 26 s on the build platform 28 to an elevated temperature. This elevated temperature is a temperature that is higher than a temperature of a layer 22 to be transfused onto the part 26 and the temperature of the belt 24. Further, in some embodiments described further below, pre-transfusion heater 74 is configured to rapidly heat the top surfaces of the 3D part 26 p and support structure 26 s to at least the melt temperature of the part material, but below the thermal oxidation threshold.

In some embodiments, the support material 66 s, which is used to form the support structure portions 22 s and the support structure 26 s, preferably has a melt rheology that is similar to or substantially the same as the melt rheology of the part material 66 p that is used to form the part portions 22 p and the 3D part 26 p. This allows the part and support materials 66 p and 66 s of the layers 22 p and 22 s to be heated together with the heater 72 to, for example, substantially the same transfer temperature. Thus, the part portions 22 p and the support structure portions 22 s may be transfused together to the top surfaces of the 3D part 26 p and the support structure 26 s in a single transfusion step as the combined layer 22 where heat in the top layers of part 26 p and support structure 26 s is rapidly diffused into the cooler layers 22 to heat the layers 22 to a temperature which results in the transfusion of the layers 22 to the part 26, and consolidation of the transferred layer to eliminate pores or voids.

Post-transfusion cooler 76 of each transfusion assembly 20 is located downstream from the nip roller 70 relative to the direction 87 a in which the platen or build platform 28 is moved along the y-axis by the y-stage gantry 82, and is configured to cool the transfused layers 22. The post-transfusion cooler 76 removes sufficient amount of heat to maintain the printed structure at a thermally stable average part temperature such that the part being printed does not deform due to heating or processing conditions during the transfusion process. The post-transfusion cooler 76 removes substantially all of the heat imparted into the 3D part with transfused layer to maintain the 3D part being printed at a thermally stable average bulk part temperature. In exemplary embodiments described below, while heater 74 is configure to rapidly heat the build surface immediately prior to the transfer of a layer 22 from belt 24, cooler 76 quickly removes the heat energy from the part 26 to prevent degradation of the part material.

As mentioned above, in some embodiments, prior to building the structure 26 on the platen or build platform 28, the build platform 28 and the nip roller 70 may be heated to desired temperatures. For example, the build platform 28 may be heated to the average part temperature of 3D part 26 p and support structure 26 s (due to the close melt rheologies of the part and support materials). In comparison, the nip roller 70 may be heated to a desired transfer temperature for the layers 22 (also due to the close melt rheologies of the part and support materials).

During the printing or transferring operation, the belt 24 carries a layer 22 past the heater 72, which may heat the layer 22 and the associated region of the belt 24 to the transfer temperature. Suitable transfer temperatures for the part and support materials 66 p and 66 s of the present disclosure include temperatures that exceed the glass transition temperature of the part and support materials 66 p and 66 s, where the layer 22 is softened but not flowable.

The heating of the part surface to at least the flowable temperature of the material enables a rapid heat transfer from the part surface to the layer to be transfused to aid in fully consolidating the layer as it is transferred. The layer 22 is transfused by pressing the press component 70 against the belt 24 to sandwich the layer 22 between the belt 24 and the part 26. The higher temperature of the part 26 enables heat diffusion from the part surface into the layer 22. This, combined with the pressing of press component 70, transfuses the layer 22 to the part 26 and fully consolidates the layer, eliminating voids. The tracks or mechanical system providing the part paths along which the platens or build platforms travel must support the platens and corresponding parts with sufficient force to withstand the transfusing forces from pressing component 70. A cooler 76 is used to rapidly cool the part surface to remove the heat energy added immediately prior to transfusion. For example, the cooler 76 can cool the part surface to a temperature sufficiently cool that it is substantially non-flowing, in one embodiment below a temperature at which the at the Young's Modulus sharply declines. The tackiness of the layer 22 and pressure from the transfusion process, combined with the surface of the part 26 being heated to a flowable temperature in excess of the layer temperature, allows the heat to rapidly diffuse to the layer 22 from the top few layers of part 26 to assist in transfusion from the belt to the part being printed.

The upper range of temperature to which heater 74 heats the top layers of the build surface, which will not result in degradation of the build material, can be determined by the time and temperature dependent thermal-degradation kinetics threshold (TDKT). The TDKT is a time-temperature parameter that defines a rate of thermal degradation of a polymeric material, such as by depolymerization, backbone chain scission, pendant-group stripping, polymer cross linking, and/or oxidation processes. The thermal degradation of a material can reduce the desired physical properties of the material, such as changing the glass transition temperature, dissolution characteristics, physical appearance, adhesive properties, and the like. These effects can cause defects in the part being printed.

The TDKT reaction rate typically follows the first-order Arrhenius equation, which is substantially linear with time and exponential with temperature. As an example, for a material exposed to a selected elevated temperature for a selected duration, increasing the exposure temperature by a small amount (e.g., about 10° C.) or reducing the exposure duration by about 50% (e.g., doubling the flow rate) may net about the same thermal reaction rates on the support material, although the particular net thermal effects may vary depending on the support material composition.

It should be understood that the example temperatures discussed herein are for ABS materials. However, the use of other materials will use different temperatures without departing from the scope of the disclosure.

After the part structure 26 is completed on the build platform 28, the structure 26 may be removed from the system 10 and undergo one or more operations to reveal the completed 3D part 26 p. For example, the support structure 26 s may be sacrificially removed from the 3D part 26 p using an aqueous-based solution such as an aqueous alkali solution. Under this technique, the support structure 26 s may at least partially dissolve or disintegrate in the solution separating the support structure 26 s from the 3D part structure 26 p in a hands-free manner. In comparison, the part 26 p is chemically resistant to aqueous solutions including alkali solutions. This allows the use of an aqueous alkali solution for removing the sacrificial support 26 s without degrading the shape or quality of the 3D part 26 p. Furthermore, after the support structure 26 s is removed, the 3D part 26 p may undergo one or more additional processes, such as surface treatment processes.

Referring to FIG. 2, a system 100 is illustrated schematically. System 100 represents a transfer system of an exemplary electrophotography-based additive manufacturing system for printing 3D parts and associated support structures, in accordance with embodiments of the present disclosure. System 100 includes a transfusion assembly 162, represented by only the nip roller/pressing component. It will be understood by those of skill in the art that in addition to a pressing component (such as pressing component 70), transfusion assembly 162 also typically includes a transfer medium (such as belt 24), a pre-transfusion heater (such as heater 72) for pre-heating developed layers, a pre-transfusion heater (such as heater 74) for pre-heating a part build surface, and a post-transfusion cooler (such as cooler 76) for cooling the transfused layers and part. Transfusion assembly 162 can also be considered to include any EP engines for generating the developed layers as discussed above, as separate illustrations of the EP engines and other transfusion assembly components are omitted to simplify illustration of disclosed concepts.

System 100 includes a track or rail mechanism 151 which can be used as type of x-stage of a gantry system 153 a in place of the gantry 80 of the conventional single EP/transfuser system such as is illustrated in FIG. 1A, and is configured to provide multipath capabilities. As illustrated, two parts 152 and 154 are being printed at the same time. The parts 152 and 154, and supporting build platens 153 and 155, move in the x-direction on a single rail 170 of a track mechanism 151 of a gantry 152 a. System 100 includes two separate x-stage actuators or “x forcers” represented at 172 and 174, each of which moves a corresponding one of part/platen 152/153 and part/platen 154/155 independently in the x-direction on rail 170. Both of parts 152 and 154 are moved under a single transfusion assembly 162, with the path of each part/platen covering overlapping portions of the total length of rail 170 such that each part/platen can be both moved under (or proximate) the single transfusion assembly and can be moved toward a respective one of the ends of rail 170 to allow the other part/platen to be moved under/proximate the EP/transfuser.

The system 100 shown in FIG. 2, implementing a multipath configuration by adding a second x forcer to the existing single x-rail 170, supports a longer platen length. Additionally, one of the two platens can be parked at a distant end of the x-stage rail 170 while the other part continues building, so that the parked platen can have its part removed or reloaded (or inspected, or planed). System 100 provides increased productivity, but also requires a substantial increase in footprint of the system. Even retaining a single transfusion assembly with a single trajectory, there are advantages of having two active build platens supplied by an engine system. When parts travel along the same linear path, they experience the same linear thermal directionality and history, providing consistency in part manufacture. Also, part removal, new build sheet mounting, and planing could be performed on either end of the single stage travel to one part, while the other part continued to be processed. Further, using a track or rail system with separate platens 153 and 155 allows different sized and dimensioned platens to be utilized for different sized parts to be printed. The platens 153 and 155 need not be of the same sizes in all embodiments.

System 100 includes a track or rail mechanism 151 which can be used as type of x-stage of a gantry system 153 a in place of the gantry 80 of the conventional single EP/transfuser system such as is illustrated in FIG. 1A, and is configured to provide multipath capabilities. As illustrated, two parts 152 and 154 are being printed at the same time. The parts 152 and 154, and supporting build platens 153 and 155, move in the x-direction on a single rail 170 of a track mechanism 151 of a gantry 153 a.

Referring to FIG. 3, a system 200 is illustrated schematically. System 200 is another exemplary transfer assembly of an electrophotography-based additive manufacturing system for printing 3D parts and associated support structures, in accordance with embodiments of the present disclosure. System 200 is also configured to provide multipath capabilities using a track or rail mechanism 251 which can be used as type of x-stage of a gantry system 253 a in place of the gantry 80 of the conventional single EP/transfuser system such as is illustrated in FIG. 1A, and is configured to provide multipath capabilities. As illustrated, two parts 252 and 254 are being printed at the same time. The parts 252 and 254, and supporting build platens 253 and 255, each move on a separate one of two x-stages or rails 270 and 271, of track or rail mechanism 251 of gantry system 253 a, mounted in parallel and configured to toggle or move in the y-direction such that first one x-stage is positioned under a single transfusion assembly 262, and then the other x-stage is positioned under the transfusion assembly 262. The parts 252 and 254, and supporting build platens 253 and 255, move in the x-direction each on a separate one of the two x-stages or rails 270 and 271 of gantry system 253 a. By toggling or moving the two rails or x-stages 270 and 271, each of parts 252 and 254 are moved under a single transfusion assembly 262 one at a time. In FIG. 3, second positions of rails or x-stages 270 and 271, moved in the y-direction to alternate which of parts 252 and 254 are positioned under transfusion assembly 262, are represented at 270-1 and 271-1, respectively.

In some exemplary embodiments, track or rail mechanism 251 of gantry system 253 a having the two x-stages can be implemented with a single z-stage such that both x-stages and the corresponding parts move together in the y-direction, though this need not be the case in all embodiments. In alternate embodiments, each of the two x-stages can have a separate z-stage and move in the z-direction independent of the other. In system 200, wiring of the gantry system need not be substantially more complex than conventional systems with only a single x-stage. However, the system 200 can provide the advantage, in comparison to a single x-stage system, of increased utilization of the EP engines using a minimal number of additional components. System 200 can be used to implement parallel build of two parts in some embodiments.

Referring to FIG. 3A, a system or transfer assembly 500, of an electrophotography-based additive manufacturing system for printing 3D parts and associated support structures in accordance with embodiments of the present disclosure, is schematically illustrated. The transfer assembly 500 includes a nip roller 502 that is fixed in a stationary position but rotates about an axis of rotation. Typically, a belt is positioned about the nip roller 502, however the belt has been omitted to simplify the illustration. Further, the EP imaging of the layers is performed as discussed above.

The transfer assembly 500 includes a gantry 504 and two build platforms or x stages 506 and 508 that move independent of each other in an x-direction (a direction that is tangential to a lower portion of the nip roller of transfusion assembly 502 in a print plane). The stage 506 is positioned on rails 510 and is moved in the x-direction by rotating a threaded shaft 512. The stage 508 has a similar configuration to that of the stage 506 and includes rails 514 and a threaded shaft 516 that engages a threaded bore in the stage to move the stage 508 in the x-direction. As the two shafts 512 and 516 can be manipulated and controlled independent of each other, the movement of the stages 506 and 508 in the x-direction can be controlled independent of each other.

The x stage 506 is secured to front left and right y stages 520 and 522. Similarly, the x stage 508 is secured to back, left and right stages 524 and 526. The front, left y stage 520 and the back, left y stage 524 are positioned on rails 530 and a threaded rod 532 threadably engages apertures in both the front, left y stage 520 and the back, left y stage 524 such that the left y stages move in unison. The front, right y stage 522 and the back, right y stage 526 are positioned on rails 534 and a threaded rod 536 threadably engages apertures in both the front right y stage 522 and the back, right y stage 526 such that the left y stages 522 and 526 move in unison.

The gantry 504 also indexes the x stages 506 and 508 down a single layer thickness in the z-direction once imaged layers are transfused onto both x stages 506 and 508. The threaded rods 532 and 536 are controlled such that the x stages 506 and 508 move in unison in the y-direction. However, the x stages 506 and 508 can be independently controlled in the y direction. Further, it is within the scope of the present disclosure to utilize three or more x stages and utilizing a gantry having different configures to control the movement of the stages in the x, y and z directions.

By having two such x stages 506 and 508, and toggling back-and-forth between the two x stages 506 and 508 for each image, the utilization of the EP engines can be brought closer to 80% of utilization. The disclosed gantry 504 also has the advantage that the part moves through transfusion in one direction and at one velocity. As a result, each point on the surface of the part has the same temporal thermal experience, which is important for metrology and part strength.

It is also within the scope of the present disclosure to utilize a single x stage that is longer than the x stage disclosed above, where the single x stage can support several moving platens. Similar to the above disclosed duel x stage, a single x stage with multiple platens does allow for part removal and restart at either end of the stage while processing continues on the secondary platen.

Referring to FIG. 4, a system or transfer assembly 300, of an electrophotography-based additive manufacturing system for printing 3D parts and associated support structures in accordance with embodiments of the present disclosure, is illustrated schematically. System 300 is also configured to provide multipath capabilities using a gantry system 302 a with one or more continuous “racetrack” paths, provided by tracks or rails 310, to move parts 302 and 304, and corresponding platens 303 and 305, in the x-direction and y-direction. Such a configuration can provide benefits as compared to implementing three or more independent x-stages on a large common z-stage. Enabling the platens/parts to maneuver continuously around a singular or multiple track(s) 310 can provide process throughput advantages.

The track 310 can be moved in the z-direction using a single z-stage actuator or actuation mechanism 307of the gantry system, similar to mechanism 83 as shown in FIG. 1A. However, the stages can no longer be hard-wired to power supplies or controllers. Instead, in some exemplary embodiments, the stages are preferably powered by slip contacts. In the alternative, the stages can be powered wirelessly or by battery. Signaling to the stages (to, for example, set and measure the platen temperature) is preferably done wirelessly, such as by Wi-Fi or Bluetooth, in some embodiments. In alternative embodiments, instead of mounting the entire continuous loop of track 310 on a single z-stage, each platen 303, 305 can be mounted to track 310 on a separate agile z-stage actuation mechanism 307-1, 307-2 so that movement of each part in the z-direction is independent of other parts, and different part heights can be accommodated. By having agile z stages to each active traveling platen, difficulties with z-information will be minimized. This provides the throughput advantage of the double x-stage system shown in FIG. 3, but with lesser accelerations required to shuttle the stages back and forth every few seconds.

Referring to FIG. 5, a system or transfer assembly 350, of an electrophotography-based additive manufacturing system for printing 3D parts and associated support structures in accordance with embodiments of the present disclosure, is illustrated schematically. As illustrated five parts 352, 354, 356, 358 and 360 are being printed at the same time. The parts 352-360 move on independent, branched paths of a track or rail mechanism 351 to provide the necessary processing at certain locations. For instance, transfusion assemblies 362 and 364 are used to transfer layers of materials to the parts being built. Refining unit 366, such as a planer, can be utilized to refine the part while being printed. Inspection unit 368 can also be utilized to determine the metrology of the parts being printed. Each part 352-360 is positioned on a respective one of build platens 353, 355, 357, 359 and 361, and the build platens and parts are independently movable on respective ones of gantries 352 a, 354 a, 356 a, 358 a and 360 a such that parts of different heights can be printed at the same time. With the gantries 352 a, 354 a, 356 a, 358 a and 360 a, each part is provided with a separate z-direction elevator or actuation mechanism (see e.g., z-stage actuation mechanism 83 shown in FIG. 1A) and linear motion on the branched paths. An important improvement or feature enabling many additional functions is provided by including a separate z-stage in the individual gantries for each part/platen. The mass that each z-stage is required to move/manipulate is reduced by almost four orders of magnitude in some embodiments as compared to some single z-stage embodiments. This allows the z-location of the rails and processing apparatus to be rigid.

While planers and metrology units are illustrated at 366 and 368, other processing units can also be utilized, including but not limited to, heat transfer, cleaning, queueing, annealing, vapor smoothing, support dissolution, milling, graphite sheet insertion, plating, chemical vapor deposition, and test structure destructive testing. With system 350, the multiple pathways and separate z-direction movement for each part allows implementation of a variety of processes in parallel on multiple parts as part of a manufacturing process flow. Implementing different types of processes on the parts can be implemented in an efficient process flow, with both fast and slow paths, in series and in parallel.

More complex trajectories such as shown in FIG. 5 offer less improvement in utilization, but more capabilities such as adding metrology and subtractive processing, as well as the ability to shuttle parts to other transfusion assemblies (to allow maintenance, refilling, or alternative materials or particle size distributions). In some exemplary disclosed embodiments having independent z-stages in the gantry for each part provides advantages as discussed above. However, in some embodiments, if two transfusion assemblies are configured in a multi-part system, it may be preferable that each transfusion assembly be on its own z-stage, with the remaining components (e.g., platens/parts) being at a fixed z location. This need not be the case in all embodiments. However, once the number of required z-stages exceeds two, it may become increasingly preferable for each part/platen/mini-environment to have its own z-stage.

In an example conventional EP-based additive manufacturing system, many EP engines (e.g., five EP engines) may feed one transfuser. Two independent EP/transfusers has significant advantage for up-time and reliability, as one can be maintained as the other continues. The combination offers higher build rate, or access to more materials. For example, if a factory floor included a large number (e.g., 100) of EP/transfusers, the manufacturing process could be implemented similarly to semiconductor fabrication, and a rail system can be configured and used to allow a part/platen/z-stage/mini-environment access to any of those EP/transfusers.

Disclosed embodiments allow multiple additive processes to be implemented as part of a manufacturing process flow or system. In EP-based additive manufacturing systems, material is added with EP transfusion. A second desirable additive step is painting, such as coloring with a robotic ink jet head. Other additive steps that can be implemented include low melt alloys being dispensed into cavities in the part-in-process, metals being electroplated or applied by chemical vapor deposition, high temperature polymers being applied by fusion deposition modeling, inserts such as RFID tags being applied, for example.

Also, with the decoupling of the linear engine/transfusion process, the capability then exists for adding substrate materials as optional layers within a part, including substrate materials made from fiberglass, high temperature glass fibers, boron fibers, graphite or carbon fibers. These fibers would remain incorporated into the fused toner stack.

Also, with disclosed embodiments, subtractive processes can be implemented as well. For example, a planer subtractive process, a support removal subtractive process, a 3-axis (or 5-axis) mill subtractive process (to allow significant improvement in fiducial position for accurate parts) or a laser oblation subtractive process (to add finer resolution detail) can be implemented as part of the process flow.

Also, with disclosed embodiments, metrology processes can be implemented in-situ as well. There are numerous measurements presently accompanying EP/transfuse; these are constrained to be compatible with the speeds and temperatures of conventional EP processes. Dimensional metrology matters to many users. This can be measured at known part temperatures photographically or by mechanical contact. Part strength can be measured destructively or non-destructively. Density, conductivity, color, water content, residual strain, and elongation can also be measured, for example.

Referring now to FIG. 6, shown is a diagrammatic illustration of a chamber 400 configured to enclose the part(s)-in-process in a controlled environment so that it can transit between remote processes, such as those discussed above, while remaining at a known temperature distribution, water content, and cleanliness. In exemplary embodiments, chamber 400 is configured to be environmentally controlled for at least temperature and relative humidity, though other environmental conditions can be controlled as well. Chamber 400 is an optional device which can be used to add an additional step, in the above-described sequences, of optionally enclosing the part-in-process in a controlled environment. The part-in-process from a chamber 400 can then re-enter the racetrack or the branched paths at a desired process step. The mini-environment can, in some embodiments, also store and supply carbon fiber or other sheets in a stacked fashion, or store in-process multi-layer parts which require movement to another processing station or to be re-incorporated into one of the processes of the racetrack or branched paths.

Commonly owned U.S. Patent Publication No. U.S. 2017/0192382 to Baecker, entitled ELECTROPHOTOGRAPHIC ADDITIVE MANUFACTURING WITH MOVING PLATEN AND ENVIRONMENTAL CHAMBER, describes control of the local environment of a build area (with an open top), and is herein incorporated by reference in its entirety. Chamber 400 can be configured to provide control such as described therein.

In some of the various embodiments as described above, the independent Z-stages are not rigidly linked to neighboring z-stages, but instead are allowed to move separately of the neighboring z-stages.

In some embodiments, the average temperature of the part build plane and the temperature of the platen are maintained by the process-controlled environment to meet the requirements of the individual process stage. As such, the temperatures may be different, depending on the process type. The platen may also accommodate temperature control capability. To aid in separate temperature control.

In some embodiments, since the racetrack or branched paths may contain a variety of non-sequential new unit operations, vacuuming (removing transferred but un-fused toner) can be a useful additional processing step after transfuse and before the subsequent part re-heating. The just-transferred layer will typically be only lightly adhered to the part build surface, and can be removed, for example, with shearing air. Such a process step can be useful for exposing a surface for inspection, re-filling areas with non-EP-able powders, or re-filling areas with liquids (such as low-melt alloys).

Referring now to FIG. 7, shown is one exemplary embodiment of a method 500 for printing a part using an electrophotographic (EP) or electrostatographic additive manufacturing system in accordance with embodiments and concepts discussed above. Disclosed methods, such as shown in FIG. 7, are implemented for example in suitably configured or programmed controllers such as controllers 36 and/or 38 in exemplary systems. As shown at block 502, digital models of the 3D parts to be printed are obtained, and at block 504, the digital models are sliced. The digital model slices can then be stored on a computer readable medium and/or output for printing on an EP or electrostatographic manufacturing system. While in some embodiments method 500 includes steps such as represented at blocks 502 and 504, in other embodiments such steps can be omitted and the method can instead begin with obtaining sliced digital model data.

At block 506, layers 22 of a powder material are developed using at least one EP or electrostatographic imaging engine 12. The developed layers are optionally transferred at block 508 from the one or more engines to a transfer medium such as transfer belt 24. In other embodiments, the developed layers are transferred directly to a part surface, and a transfer medium such as belt 24 is not required. Next, functions represented at blocks 510, 512, 514 and 516 are performed repeatedly, for each of multiple developed layers to be transferred to build surfaces of the parts on two separate platens or build platforms such that two separate parts are built in parallel using a first transfusion assembly by transfusing layers on the two parts in accordance with some form of alternating pattern. At block 510, the part transport system is used to move a first platen proximate to a first transfusion assembly. At block 512, the first transfusion assembly is used to transfuse an imaged layer from the transfer medium to the part build surface of a first part on the first platen. Then, at block 514 the transport system is used to move a second platen proximate the first transfusion assembly, and a block 516 the first transfusion assembly is used to transfuse another of the plurality of imaged layers from the first transfer medium onto a part build surface of a second part on the second platen.

At decision 518, a determination is made as to whether the last layer to be transfused to a part has been processed. If the last layer has not been processed, then the process returns to step 510 and the process repeats itself until the last layer has been transfused and the process terminates at block 520.

It must be understood that method of alternating the use of a first transfusion assembly to transfuse layers onto different parts can be extended to more than two parts. In some such embodiments, additional steps or functions can be implemented between block 510 and decision 518. Further, in some embodiments, more than one transfusion assembly can be used in a system and developed layers can be transfused onto a part build surface of a part by multiple transfusion assemblies in some alternating pattern as well. Steps accommodating such embodiments can also be added, for example, between block 516 and decision 518, in method 500 shown in FIG. 7.

In some exemplary embodiments, the image engines or EP engines are configured to deposit directly onto the part build surface, avoiding the need for the transfer medium belt. In these cases, the part itself may serve as the transfer medium, moving from EP engine to EP engine. FIGS. 8 and 9 illustrate exemplary EP engine configurations for such embodiments, while FIG. 10 illustrates two EP engines 712-1 and 712-2 configured to develop image layers directly on build surfaces of parts (see e.g., parts 626-1 and 626-2 moving on track 610 on build platforms or platens 603 and 605, while a single transfusion assembly 720 transfuses the image layers deposited on the parts by the EP engines 712-1 and 712-2 as the parts move from EP engine to transfuser assembly. In other embodiments, multiple transfusion assemblies can be used, and tracks with additional paths can be used. Further, the z-stage actuators discussed above are omitted from FIG. 10 for ease of illustration.

Referring again to FIG. 8, illustrated are EP engines 612 p and 612 s, where EP engine 612 s (i.e., the upstream EP engine relative to the direction of movement of parts 626-1 and 626-2 on platens or build platforms 628-1 and 628-2 on track or rail 610) develops layers of the support material, and EP engine 612 p develops layers of the part material. In alternative embodiments, the arrangement of EP engines 612 p and 612 s may be reversed such that EP engine 612 p is upstream from EP engine 612 s.

In the shown embodiment, EP engines 612 p and 612 s may include the same components, such as photoconductor drum 642 having conductive drum body 644 and photoconductive surface 646. Conductive drum body 644 is an electrically-conductive drum (e.g., fabricated from copper, aluminum, tin, or the like) that is electrically grounded and configured to rotate around shaft 648. Shaft 648 is correspondingly connected to drive motor 650, which is configured to rotate shaft 648 (and photoconductor drum 642) in the direction of arrow 652 at a constant rate.

Photoconductive surface 646 is a thin film extending around the circumferential surface of conductive drum body 644, and is preferably derived from one or more photoconductive materials, such as amorphous silicon, selenium, zinc oxide, organic materials, and the like. As discussed below, surface 646 is configured to receive latent-charged images of the sliced layers of the 3D part or support structure (or negative images), and to attract charged particles of the part or support material to the charged or discharged image areas based on the Q/M ratios of the materials, thereby creating the layers of the 3D part or support structure (and preferably a fiducial structure, as discussed below).

As further shown, EP engines 612 p and 612 s also includes charge inducer 654, imager 656, development station 658, cleaning station 660, and discharge device 662, each of which may be in signal communication with controller assembly 38 (discussed with reference to FIG. 1). Charge inducer 654, imager 656, development station 658, cleaning station 660, and discharge device 662 accordingly define an image-forming assembly for surface 646 while drive motor 650 and shaft 468 rotate photoconductor drum 642 in the direction of arrow 652.

In the shown example, the image-forming assembly for surface 646 of EP engine 612 s is used to form layers 664 s of the support material (referred to as support material 666 s), where a supply of support material 666 s may be retained by development station 658 (of EP engine 612 s) along with carrier particles. Similarly, the image-forming assembly for surface 646 of EP engine 612 p is used to form layers 664 p of the part material (referred to as part material 666 p), where a supply of part material 666 p may be retained by development station 658 (of EP engine 612 p) along with carrier particles.

As further shown in FIG. 8, each layer 664 p may include a fiducial segment 664 f of the part material 666 p. As discussed below, fiducial segment 664 f preferably has known dimensions and a preset location that is offset and separate from the remaining portions of layers 664 p and 664 s. In some alternative embodiments, support layer 664 s may also include a fiducial segment of the support material 666 s, where the support material fiducial portion may be formed in combination with, or as an alternative to fiducial segment 664 f.

Controller assembly 38 may generate fiducial segments 664 f by modifying the bitslices used to generate layer 664 p. For example, controller assembly 38 may add bitslice pixels for fiducial segments 664 f at coordinate locations that are outside the bounding boxes of layer 664 p, but still within the usable build volume of the system. This allows each fiducial segment 664 f to be offset and separate from the remaining portion of layer 664 p and from layer 664 s. In the shown example, fiducial segment 664 f is developed at the leading end of layer 664 p.

Charge inducer 654 is configured to generate a uniform electrostatic charge on surface 646 as surface 646 rotates in the direction of arrow 652 past charge inducer 654. Suitable devices for charge inducer 654 include corotrons, scorotrons, charging rollers, and other electrostatic charging devices.

Imager 656 is a digitally-controlled, pixel-wise light exposure apparatus configured to selectively emit electromagnetic radiation toward the uniform electrostatic charge on surface 646 as surface 646 rotates in the direction of arrow 652 past imager 656. The selective exposure of the electromagnetic radiation to surface 646 corresponds to the associated bitslices received from controller assembly 38, and causes discrete pixel-wise locations of the electrostatic charge to be removed (i.e., discharged to ground), thereby forming latent image charge patterns on surface 646.

Suitable devices for imager 656 include scanning laser (e.g., gas or solid state lasers) light sources, light emitting diode (LED) array exposure devices, and other exposure device conventionally used in 2D electrophotography systems. In alternative embodiments, suitable devices for charge inducer 654 and imager 656 include ion-deposition systems configured to selectively directly deposit charged ions or electrons to surface 646 to form the latent image charge pattern. As such, as used herein, the term “electrophotography” includes ionography.

Each development station 658 is an electrostatic and magnetic development station or cartridge that retains the supply of part material 666 p or support material 666 s, preferably in powder form, along with carrier particles. Development stations 658 may function in a similar manner to single or dual component development systems and toner cartridges used in 2D electrophotography systems. For example, each development station 658 may include an enclosure for retaining the part material 666 p or support material 666 s and carrier particles. When agitated, the carrier particles generate triboelectric charges to attract the powders of the part material 666 p or support material 666 s, which charges the attracted powders to a desired sign and magnitude based on their Q/M ratios.

Each development station 658 may also include one or more devices for transferring the charged part material 666 p or support material 666 s to surface 646, such as conveyors, fur brushes, paddle wheels, rollers, and/or magnetic brushes. For instance, as surface 646 (containing the latent charged image) rotates from imager 656 to development station 658 in the direction of arrow 652, the charged part material 666 p or support material 666 s is attracted to the appropriately charged regions of the latent image on surface 646, utilizing either charged area development or discharged area development (depending on the electrophotography mode being utilized).

This creates successive layers 664 p or 664 s as photoconductor drum 612 continues to rotate in the direction of arrow 652, where the successive layers 664 p or 664 s correspond to the successive bitslices of the digital model of the 3D part or support structure. After being developed, the successive layers 664 p or 664 s are then rotated with surface 466 in the direction of arrow 652 to a transfer region in which layers 664 p or 664 s are successively transferred from photoconductor drum 642 to the build surface of part 626. While illustrated as a direct engagement between photoconductor drum 642 and part 626, in some preferred embodiments, EP engines 612 p and 612 s may also include intermediary transfer drums and/or belts, as discussed further below in FIG. 9.

After a given layer 664 p or 664 s is transferred from photoconductor drum 42 to part 626 (or an intermediary transfer drum or belt), drive motor 650 and shaft 648 continue to rotate photoconductor drum 642 in the direction of arrow 652 such that the region of surface 646 that previously held the layer 664 p or 664 s passes cleaning station 660. Cleaning station 660 is a station configured to remove any residual, non-transferred portions of part or support material 666 p or 666 s. Suitable devices for cleaning station 660 include blade cleaners, brush cleaners, electrostatic cleaners, vacuum-based cleaners, and combinations thereof.

After passing cleaning station 660, surface 646 continues to rotate in the direction of arrow 652 such that the cleaned regions of surface 646 pass discharge device 662 to remove any residual electrostatic charge on surface 646, prior to starting the next cycle. Suitable devices for discharge device 662 include optical systems, high-voltage alternating-current corotrons and/or scorotrons, one or more rotating dielectric rollers having conductive cores with applied high-voltage alternating-current, and combinations thereof.

In some embodiments, one or both of EP engines 612 p and 612 s may also include one or more intermediary transfer drums and/or belts between photoconductor drum 642 and parts 626. For example, as shown in FIG. 9, EP engine 612 p may also include intermediary drum 642 a that rotates an opposing rotational direction from arrow 652, as illustrated by arrow 652 a, under the rotational power of motor 650 a. Intermediary drum 642 a engages with photoconductor drum 642 to receive the developed layers 664 p from photoconductor drum 642, and then carries the received developed layers 664 p and transfers them to the build surface of part 626.

EP engine 612 s may include the same arrangement of intermediary drum 642 a for carrying the developed layers 664 s from photoconductor drum 642 to part 626. The use of such intermediary transfer drums or belts for EP engines 612 p and 612 s can be beneficial for thermally isolating photoconductor drum 642 from part 626, if desired.

A strategic advantage of ‘racetrack’, or ‘simultaneous/parallel build’, that is distinct from typical serial processing of batches, is that data acquired from down-stream steps (like top-of-part height after transfuse) can be fed back to up-stream steps (like adjusting the M/A(x,y) of the imaging engines) with just one or two layers of delay. If a different method of breaking up the monolithic printer is used (like printing every layer first in one machine, then transfusing them to form a part in another machine), there is no opportunity to feed-back such intermediate measurements.

Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the disclosure. 

What is claimed is:
 1. An electrostatographic based additive manufacturing system for printing three-dimensional parts, the additive manufacturing system comprising: a first imaging engine configured to develop imaged layers of a thermoplastic-based powder; a first transfer medium configured to receive the imaged layers from the first imaging engine; a first transfusion assembly configured to transfuse imaged layers from the first transfer medium onto part build surfaces by pre-heating an imaged layer on the first transfer medium and applying pressure to transfuse the pre-heated imaged layer onto a part build surface; a first platen configured to have a first part formed thereon; a second platen configured to have a second part formed thereon; and a part transport system providing part paths, the part transport system configured to move the first platen and the second platen proximate the first transfusion assembly in an alternating pattern such that the first part and the second part are each acted on by the first transfusion assembly to have imaged layers transferred thereto to build the first part and the second part in parallel.
 2. The electrostatographic based additive manufacturing system of claim 1, wherein part transport system includes at least one track providing the part paths.
 3. The electrostatographic based additive manufacturing system of claim 1, and further comprising: a second imaging engine configured to develop imaged layers of the thermoplastic-based powder; a second transfer medium configured to receive the imaged layers from the second imaging engine; a second transfusion assembly configured to transfuse imaged layers from the second transfer medium onto part build surfaces by pre-heating an imaged layer on the second transfer medium and applying pressure to transfuse the pre-heated imaged layer onto a part build surface; wherein the part transport system is configured to move the first platen and the second platen proximate the first transfusion assembly and proximate the second transfusion assembly in an alternating pattern such that the first part and the second part are each acted on by the first transfusion assembly and the second transfusion assembly to have imaged layers transferred thereto to build the first part and the second part in parallel.
 4. The electrostatographic based additive manufacturing system of claim 1, and further comprising a plurality of decoupled processing stations, wherein the part transport system is configured to move the first platen and the second platen proximate the plurality of decoupled processing stations such that the first part and second part are built in parallel at the plurality of decoupled processing stations.
 5. The electrostatographic based additive manufacturing system of claim 1, wherein the part transport system includes a gantry with a single x-stage having at least two x-stage actuators each configured to move a different one of the first platen and the second platen under the first transfusion assembly.
 6. The electrostatographic based additive manufacturing system of claim 1, wherein the part transport system includes a gantry with a first x-stage and a second x-stage each configured to move a different one of the first platen and the second platen in the x-direction, the system configured to move the first and second x-stages in a y-direction such that the first x-stage is positioned proximate the first transfusion assembly and then the second x-stage is positioned proximate the first transfusion assembly.
 7. The electrostatographic based additive manufacturing system of claim 6, wherein the first x-stage and the second x-stage are mounted in parallel.
 8. The electrostatographic based additive manufacturing system of claim 1, wherein the part transport system includes a track along which the first platen and the second platen move in both an x-direction and a y-direction perpendicular to the x-direction.
 9. The electrostatographic based additive manufacturing system of claim 8, and further comprising a single z-stage configured to move the track in a z-direction perpendicular to the x-direction and the y-direction.
 10. The electrostatographic based additive manufacturing system of claim 8, and further comprising a plurality of z-stages each configured to move a different one of the plurality of platens in a z-direction, perpendicular to the x-direction and the y-direction, relative to the track.
 11. The electrostatographic based additive manufacturing system of claim 1, wherein the first transfusion assembly comprises a pre-transfusion heater, a pressing component, and a post-transfusion cooler.
 12. A method for printing a three-dimensional part with an electrostatographic based additive manufacturing system, the method comprising: developing layers of a powder material using at least one electrostatographic engine; transferring the developed layers from the at least one electrostatographic engine to a transfer medium; using a transport system to move a first platen proximate a first transfusion assembly; using the first transfusion assembly to transfuse one of a plurality of imaged layers from the first transfer medium onto a part build surface of a first part on the first platen; using the transport system to move a second platen proximate the first transfusion assembly; using the first transfusion assembly to transfuse another of the plurality of imaged layers from the first transfer medium onto a part build surface of a second part on the second platen such that the first part and the second part are built in parallel.
 13. The method of claim 12, and further comprising alternating, for subsequent layers of the plurality of imaged layers, using the transport system to move the first platen proximate the first transfusion assembly and using the first transfusion assembly to transfuse a subsequent one of the plurality of imaged layers from the first transfer medium onto the part build surface of the first part on the first platen with using the transport system to move the second platen proximate the first transfusion assembly and using the first transfusion assembly to transfuse a subsequent one of the plurality of imaged layers from the first transfer medium onto the part build surface of the second part on the second platen such that the first part and the second part are built in parallel.
 14. The method of claim 12, wherein using the first transfusion assembly to transfuse the one of the plurality of imaged layers from the first transfer medium onto the part build surface of the first part on the first platen further comprises pre-heating the one of the plurality of imaged layers on the first transfer medium and applying pressure to transfuse the pre-heated one of the plurality of imaged layers onto the part build surface of the first part.
 15. An electrostatographic based additive manufacturing system for printing three-dimensional parts, the additive manufacturing system comprising: a first imaging engine configured to develop imaged layers of a thermoplastic-based powder on a part build surface; a first transfusion assembly configured to transfuse imaged layers on the part build surfaces by heating an imaged layer on the part build surface and applying pressure to transfuse the heated imaged layer into the part build surface; a first platen configured to have a first part formed thereon; a second platen configured to have a second part formed thereon; and a part transport system providing part paths, the part transport system configured to move the first platen and the second platen proximate the first imaging engine and the first transfusion assembly in an alternating pattern such that the first part and the second part are each acted on by the first imaging engine and the first transfusion assembly to have imaged layers transferred thereto to build the first part and the second part in parallel. 